The present invention relates to a gas purge method which is preferably applied to an exposure apparatus that uses ultraviolet rays as exposure light, purges the interior of the apparatus with gas, and projects the pattern of a master such as a mask onto a photosensitive substrate via a projection optical system, and which purges with gas a pellicle space defined by a master and a pellicle used to prevent deposition of a foreign matter on a pattern surface. The present invention also relates to an exposure apparatus having a gas purge apparatus for purging the pellicle space with gas.
A conventional manufacturing process for a semiconductor element such as an LSI or a VLSI formed from a micropattern uses a reduction type projection exposure apparatus for printing and forming by reduction projection a circuit pattern drawn on a master such as a mask onto a substrate coated with a photosensitive agent. With an increase in the packaging density of semiconductor elements, demands have arisen for further micropatterning. Exposure apparatuses are coping with micropatterning along with the developing of a resist process.
A means for increasing the resolving power of the exposure apparatus includes a method of changing the exposure wavelength to a shorter one, and a method of increasing the numerical aperture (NA) of the projection optical system.
As for the exposure wavelength, a KrF excimer laser with an oscillation wavelength of 365-nm i-line to recently 248 nm, and an ArF excimer laser with an oscillation wavelength around 193 nm have been developed. A fluorine (F2) excimer laser with an oscillation wavelength around 157 nm is also under development.
An ArF excimer laser with a wavelength around ultraviolet rays, particularly, 193 nm, and a fluorine (F2) excimer laser with an oscillation wavelength around 157 nm are known to have an oxygen (O2) absorption band around their wavelength band.
For example, a fluorine excimer laser has been applied to an exposure apparatus because of a short wavelength of 157 nm. The 157-nm wavelength falls within a wavelength region called a vacuum ultraviolet region. In this wavelength region, light is greatly absorbed by oxygen molecules, and hardly passes through the air. The fluorine excimer laser can only be applied in an environment in which the atmospheric pressure is decreased to almost vacuum and the oxygen concentration is fully decreased. According to the reference xe2x80x9cPhotochemistry of Small Moleculesxe2x80x9d (Hideo Okabe, A Wiley-Interscience Publication, 1978, page 178), the absorption coefficient of oxygen to 157-nm light is about 190 atmxe2x88x921cmxe2x88x921. This means when 157-nm light passes through gas at an oxygen concentration of 1% at one atmospheric pressure, the transmittance T per cm is only T=exp(xe2x88x92190xc3x971 cmxc3x970.01 atm)=0.150.
Oxygen absorbs light to generate ozone (O3), and the ozone promotes absorption of light, greatly decreasing the transmittance. In addition, various products generated by ozone are deposited on the surface of an optical element, decreasing the efficiency of the optical system.
To prevent this, the oxygen concentration in the optical path is suppressed to a low level on the order of several ppm order or less by a purge means using inert gas such as nitrogen in the optical path of the exposure optical system of a projection exposure apparatus using a far ultraviolet laser such as an ArF excimer laser or a fluorine (F2) excimer laser as a light source.
In such an exposure apparatus using an ArF excimer laser with a wavelength around ultraviolet rays, particularly, 193 nm, or a fluorine (F2) excimer laser with a wavelength around 157 nm, an ArF excimer laser beam or a fluorine (F2) excimer laser beam is readily absorbed by a substance. A light absorption substance in the optical path must be purged to several ppm order or less. This also applies to moisture, which must be removed to a ppm order or less.
For this reason, the interior of the exposure apparatus, particularly, the optical path of ultraviolet rays is purged with inert gas. A load-lock mechanism is arranged at a coupling portion between the inside and outside of the exposure apparatus. When a reticle or wafer is to be externally loaded, the interior of the exposure apparatus is temporarily shielded from outside air. After the impurity in the load-lock mechanism is purged with inert gas, the reticle or wafer is loaded into the exposure apparatus.
FIG. 1 is a schematic sectional view showing an example of a semiconductor exposure apparatus having a fluorine (F2) excimer laser as a light source and a load-lock mechanism.
In FIG. 1, reference numeral 1 denotes a reticle stage for setting a reticle bearing a pattern; 2, a projection optical system for projecting the pattern on the reticle onto a wafer serving as a photosensitive substrate; 3, a wafer stage which supports the wafer and is driven in the X, Y, Z, xcex8, and tilt directions; 4, an illumination optical system for illuminating the reticle with illumination light; and 5, a guide optical system for guiding light from the light source to the illumination optical system 4.
Reference numeral 6 denotes a fluorine (F2) laser serving as a light source; 7, a masking blade for shielding exposure light so as not to illuminate the reticle except for the pattern region; 8 and 9, housings which cover the exposure optical path around the reticle stage 1 and wafer stage 3, respectively; and 10, an He air-conditioner for adjusting the interiors of the projection optical system 2 and illumination optical system 4 to a predetermined He atmosphere.
Reference numerals 11 and 12 denote N2 air-conditioners for adjusting the interiors of the housings 8 and 9 to a predetermined N2 atmosphere; 13 and 14, reticle load-lock chambers and wafer load-lock chambers used to load a reticle and wafer into the housings 8 and 9, respectively; and 15 and 16, a reticle hand and wafer hand for transferring the reticle and wafer, respectively.
Reference numeral 17 denotes a reticle alignment mark used to adjust the reticle position; 18, a reticle stocker for stocking a plurality of reticles in the housing 8; and 19, a pre-alignment unit for pre-aligning the wafer.
If necessary, the overall apparatus is stored in an environment chamber (not shown). Air controlled to a predetermined temperature is circulated within the environment chamber to keep the internal temperature of the chamber constant.
FIG. 2 is a schematic sectional view showing another example of the semiconductor exposure apparatus having a fluorine (F2) excimer laser as a light source and a load-lock mechanism. In FIG. 2, the same reference numerals as in FIG. 1 denote the same parts.
The whole exposure apparatus shown in FIG. 2 is covered with a housing 20, and O2 and H2O in the housing 20 are purged with N2 gas. Reference numeral 21 denotes an air-conditioner for setting the entire housing 20 in an N2 atmosphere. In this exposure apparatus, the lens barrel of a projection optical system 2 and the internal space of an illumination optical system 4 are partitioned from the internal space (driving system space) of the housing 20, and independently adjusted to an He atmosphere. Reference numerals 13 and 14 denote a reticle load-lock chamber and wafer load-lock chamber used to load a reticle and wafer into the housing 20, respectively.
In general, a reticle is equipped with a pattern protection device called a pellicle. The pellicle prevents deposition of a foreign matter onto a reticle pattern surface, and suppresses the occurrence of defects caused by transfer of a foreign matter onto a wafer. FIG. 3 is a schematic view showing the structure of a pellicle.
A pellicle 24 is adhered to the pattern surface of a reticle 23 with an adhesive agent or the like. The pellicle 24 is made up of a support frame 25 large enough to surround the reticle pattern, and a pellicle film 26 which is adhered to one end face of the support frame 25 and transmits exposure light. If a space (to be referred to as a pellicle space hereinafter) defined by the pellicle 24 and reticle 23 is completely closed, the pellicle film may expand or contract due to the difference in atmospheric pressure between the inside and outside of the pellicle space or the difference in oxygen concentration. To prevent this, a vent hole 27 is formed in the support frame 25 so as to allow gas from flowing between the inside and outside of the pellicle space. An auto-screen filter (not shown) is attached to the ventilation path in order to prevent an external foreign matter from entering the pellicle space via the vent hole 27.
FIG. 4 is a schematic view showing an example of a reticle transfer path in the exposure apparatus shown in FIGS. 1 and 2.
In FIG. 4, reference numeral 22 denotes a foreign matter inspection device which measures the size and number of foreign matters such as dust deposited on the surface of the reticle 23 or pellicle film 26. The reticle 23 is loaded manually or by a transfer device (not shown) into the reticle load-lock chamber 13 serving as the entrance of the exposure apparatus. Since the reticle 23 and pellicle 24 are generally adhered outside the exposure apparatus, the pellicle 24 has already been adhered to the loaded reticle 23.
The interior of the reticle load-lock chamber 13 is purged with inert gas until the interior reaches an inert gas atmosphere similarly to the housing 8. After that, the reticle 23 is transferred by the reticle hand 15 to any one of the reticle stage 1, reticle stocker 18, and foreign matter inspection device 22.
As described above, an exposure apparatus using ultraviolet rays, particularly, an ArF excimer laser beam or fluorine (F2) excimer laser beam suffers from large absorption of the ArF excimer laser beam or fluorine (F2) excimer laser of its wavelength by oxygen and moisture. To obtain a sufficient transmittance and stability of an ultraviolet ray, the oxygen and moisture concentrations must be reduced and controlled strictly. For this purpose, a load-lock mechanism is arranged at a coupling portion between the inside and outside of the exposure apparatus. When a reticle or wafer is to be externally loaded, the interior of the exposure apparatus is temporarily shielded from outside air. After the impurity in the load-lock mechanism is purged with inert gas, the reticle or wafer is loaded into the exposure apparatus.
To ensure the transmittance and stability of a fluorine (F2) excimer laser beam, the whole reticle stage (wafer stage) including the end face of a projection lens and a critical dimension measurement interference optical system is housed in an airtight chamber, and the interior of the chamber is purged with high-purity inert gas. In addition, the reticle load-lock chamber is disposed adjacent to the airtight chamber in order to load/unload a wafer or reticle into/from the airtight chamber while maintaining a constant internal inert gas concentration.
A reticle loaded into the load-lock chamber bears a pellicle, and the pellicle space can communicate with outside air only through a relatively small vent hole. This structure prolongs a time required to complete purge in the pellicle space even after the interior of the reticle load-lock chamber reaches a predetermined inert gas concentration, degrading the productivity.
Japanese Patent Laid-Open No. 9-73167 discloses an invention of adhering a reticle and pellicle in advance in an inert gas atmosphere and filling the pellicle space with an inert gas at an oxygen concentration of 1% or less. However, the transmittance of 157-nm light is merely 15% per cm in atmospheric-pressure gas at an oxygen concentration of 1%. At present, the air gap between the reticle and the pellicle is about 6 mm. Even if this air gap is filled with gas at an oxygen concentration of 0.1%, the transmittance of 157-nm light at this air gap is merely 89.2%.
The total space distance of an optical path from the light source of the exposure apparatus to a wafer exceeds at least 1 m. To ensure a transmittance of 80% or more in the 1-m space, the oxygen concentration must be suppressed to 10 ppm or less, and ideally 1 ppm or less. In the pellicle space, the oxygen concentration must be 1 to 100 ppm or less in terms of the balance with another space and maintenance of the transmittance in the total space distance. This also applies to the moisture and carbon dioxide gas concentrations.
A pellicle film made of a fluorine-based resin has oxygen permeability, and the oxygen concentration is difficult to maintain in the ppm order. A reticle may be set on the reticle stage and exposed at an unsatisfactory inert gas concentration in the pellicle space. Since the inert gas concentration in the pellicle space gradually comes close to an ambient inert gas concentration on the reticle stage, the transmittance of exposure light in the pellicle space changes. As a result, a predetermined exposure amount cannot be stably obtained on a wafer, and an error such as a change in transfer pattern size may occur.
As for the vent hole of a pellicle support frame, Japanese Patent Laid-Open Nos. 6-27643 and 9-197652 disclose inventions providing intake and discharge holes. Japanese Patent Laid-Open No. 9-197652 also discloses an invention in which inert gas is supplied into a pellicle space via a vent hole formed in advance in a pellicle support frame and then the vent hole is sealed. This is, however, insufficient to purge gas in the pellicle space of a master with a pellicle loaded into an apparatus, and gas must be purged more efficiently.
The present invention has been made to overcome the conventional drawbacks, and has as its object to provide a means for effectively purging a space defined by a master and pellicle film with inert gas or the like in an exposure apparatus which uses ultraviolet rays as exposure light, purges the interior of the apparatus with inert gas or the like, and projects the pattern of a master onto a photosensitive substrate via a projection optical system.
To achieve the above object, according to the present invention, there is provided a gas purge method comprising the steps of opening a lid to perform either one of gas supply and discharge with respect to a pellicle space formed using a pellicle support frame having the freely openable/closable lid and a pellicle film, and controlling ether one of gas supply and discharge so as to make a detection value obtained by detecting a state of the pellicle space fall within a predetermined range. The gas may include any one of nitrogen gas, helium gas, and argon gas.
According to the present invention, there is provided an exposure apparatus in which a pellicle support frame which has a freely openable/closable lid and forms a pellicle space by using a pellicle film is mounted, and a pattern of a master facing the pellicle space is transferred onto a photosensitive substrate via a projection optical system, wherein the exposure apparatus incorporates a mechanism which opens/closes the lid, and a nozzle arranged by selecting at least one of a gas supply nozzle and a discharge nozzle, and at least one of gas supply and discharge is performed for the pellicle space via the selected nozzle.
According to the present invention, there is provided an exposure apparatus which uses ultraviolet rays as exposure light and projects a pattern of a mask onto a photosensitive substrate via a projection optical system, wherein a mechanism which opens/closes a lid attached to a pellicle support frame, a gas supply nozzle, and a discharge nozzle are inserted in a reticle transfer path within the exposure apparatus, and gas is supplied from the gas supply nozzle into a pellicle space and discharged from the discharge nozzle after the lid of the pellicle support frame is opened.
The exposure apparatus of the present invention may adopt the mechanism which opens/closes the lid attached to the pellicle support frame on a master, and either one of the gas supply nozzle and discharge nozzle. Gas may be supplied from the gas supply nozzle into the pellicle space after the lid of the pellicle support frame is opened. Alternatively, the pellicle space may be purged from the gas discharge nozzle to supply ambient gas from the gas inlet port of the pellicle support frame into the pellicle space.
In the exposure apparatus of the present invention, the mechanism which opens/closes the lid attached to the pellicle support frame, and the gas supply nozzle or gas discharge nozzle are desirably arranged in at least any one of a master load-lock chamber, master stocker, and master stage.
When the mechanism and nozzle are arranged in the master load-lock chamber, the interior of the master load-lock chamber is purged after a master is externally loaded into the master load-lock chamber. At almost the same time as the start of gas purge, the interior of the pellicle space can be purged with gas by opening the lid of the pellicle support frame. After the interior of the load-lock chamber is purged with clean gas, the interior of the pellicle space can also be purged with gas by opening the lid of the pellicle support frame. Entrance of a foreign matter in a clean room atmosphere into the pellicle space can be prevented.
When the mechanism and nozzle are arranged in the master stocker, the pellicle space need not be purged with gas within the master load-lock chamber in a case in which a master loaded from the master load-lock chamber into an airtight chamber is temporarily stocked in the master stocker. While the master is stocked in the master stocker, satisfactory gas purge can be achieved by opening the lid of the pellicle support frame.
When the mechanism and nozzle are arranged on the master stage, the lid of the pellicle support frame is kept open until the end of an exposure operation after a master is set on the master stage. This allows continuously purging the pellicle with gas.
In any case, the lid of the pellicle support frame is closed after purge. Since a vent hole is formed in the pellicle support frame, a pellicle does not expand or contract and can undergo foreign matter inspection and exposure. Even if a master with a pellicle is transferred into an atmosphere through the load-lock chamber after the end of exposure, entrance of a foreign matter into the pellicle space can be prevented.
The present invention may be characterized by comprising means for measuring flexure of the pellicle film. The exposure apparatus desirably further comprises flow rate detection means for detecting either one of a gas supply flow rate and a discharge flow rate, and flow rate control means for controlling the flow rate. The flow rate control means controls the flow rate so as to adjust a flexure value detected by the pellicle flexure measurement means to a predetermined value or less, thereby minimizing deformation of the pellicle film during purge. The same effects can also be attained by employing, instead of the flow rate detection means and flow rate control means, pressure detection means for detecting either one of a gas supply pressure and a discharge pressure and pressure control means for controlling either one of the gas supply pressure and the discharge pressure, or speed detection means for detecting either one of a gas supply speed and a discharge speed and speed control means.
The means for measuring flexure of the pellicle film desirably includes light-projecting means for emitting collimated light, light-receiving means formed from a sensor which measures a position of light emitted by the light-projecting means and reflected by the pellicle film, and arithmetic means for calculating flexure of the pellicle film from a light reception position. The means for measuring flexure of the pellicle film desirably includes means using any one of a limited-reflection photoelectric sensor, an electrostatic capacitance sensor, and an ultrasonic displacement sensor.
An exposure apparatus according to the present invention comprises means for measuring an impurity concentration in the pellicle space, and can perform gas purge until a gas concentration in the pellicle space reaches a predetermined purity. The means for measuring the impurity concentration can be combined with flow rate adjustment means and control means. In this case, gas purge can be adjusted to a proper flow rate in order to maintain the gas concentration in the pellicle space at a predetermined purity.
The means for measuring the impurity concentration in the pellicle space desirably includes light-projecting means for emitting light with a wavelength of not more than 200 nm, light-receiving means formed from a sensor which measures a quantity of light emitted by the light-projecting means and having passed through the pellicle space, and arithmetic means for calculating the impurity concentration from a quantity of light attenuated when light emitted by the light-projecting means passes through the pellicle space. Light from a light source of the exposure apparatus serving as a light source of the light-projecting means for emitting light with a wavelength of not more than 200 nm is preferably split and guided through an optical fiber. A light-projecting portion is desirably shared between the means for measuring flexure of the pellicle film and the means for measuring the impurity concentration in the pellicle space.
An exposure apparatus according to the present invention may be characterized in that an injection direction of gas supplied from a gas supply nozzle and a gas supply hole are arranged to be substantially aligned. An exposure apparatus according to the present invention may be characterized in that a discharge direction of gas discharged from a gas discharge nozzle and a gas discharge hole are arranged to be substantially aligned. Gas injected from the gas supply nozzle can enter the pellicle space with little resistance, the gas purge efficiency can be increased, and the purge time can be shortened.
In the exposure apparatus of the present invention, the flow direction of gas may be switched during purge in order to eliminate stagnation of gas at the inner corner or center of the pellicle support frame and promote spread of gas in the pellicle space. In any case, the gas desirably includes inert gas.
In the exposure apparatus of the present invention, the ultraviolet rays may include a laser beam from a laser serving as a light source. Examples of the laser beam are a fluorine excimer laser beam with a wavelength of 200 nm or less, and an ArF excimer laser beam.
In the exposure apparatus of the present invention, the gas which purges the optical path of the exposure light consists of one gas selected from the group consisting of nitrogen gas, helium gas, and argon gas.
The exposure apparatus of the present invention can comprise purge means for filling gas in the exposure apparatus.
The present invention can also be applied to a semiconductor device manufacturing method comprising the steps of installing manufacturing apparatuses for performing various processes, including any one of the above-described exposure apparatuses, in a semiconductor manufacturing factory, and manufacturing a semiconductor device by performing a plurality of processes using the manufacturing apparatuses. The semiconductor device manufacturing method desirably further comprises the steps of connecting the manufacturing apparatuses to a local area network, and communicating information about at least one of the manufacturing apparatuses between the local area network and an external network outside the semiconductor manufacturing factory. A database provided by a vendor or user of the exposure apparatus is preferably accessed via the external network to obtain maintenance information of the manufacturing apparatus by data communication. Alternatively, data communication is preferably performed between the semiconductor manufacturing and another semiconductor manufacturing factory via the external network to perform production management.
The present invention can also be applied to a semiconductor manufacturing factory comprising manufacturing apparatuses for performing various processes, including any one of the above-described exposure apparatuses, a local area network for connecting the manufacturing apparatuses, and a gateway for connecting the local area network to an external network outside the factory, wherein information about at least one of the manufacturing apparatuses can be communicated.
The present invention can also be applied to a maintenance method for any one of the above-described exposure apparatuses installed in a semiconductor manufacturing factory, comprising the steps of providing a maintenance database connected to an external network of a semiconductor manufacturing factory by a vendor or user of the exposure apparatus, authorizing access to the maintenance database from the semiconductor manufacturing factory via the external network, and transmitting maintenance information accumulated in the maintenance database to the semiconductor manufacturing factory via the external network.
The present invention may be characterized in that any one of the above-described exposure apparatuses further comprises a display, a network interface, and a computer which executes network software, and maintenance information of the exposure apparatus is communicated via a computer network. The network software preferably provides on the display a user interface for accessing a maintenance database which is provided by a vendor or user of the exposure apparatus and connected to the external network outside a factory where the exposure apparatus is installed, and enables obtaining information from the database via the external network.